Marine boiler



June 7, 1960 Filed Feb. 6, 1957 G. W. KESSLER MARINE BOILER 8Sheets-Sheet 1 Until L E &

INVENTOR. George W. Kessler ATTORNEY June 7, 1960 G. w. KESSLER MARINEBOILER 8 Sheets-Sheet 2 Filed Feb. 6, 1957 9 mmwmb B mm on INVENTOR.George W. Kessler ATTORNEY June 7, 1960 e. w. KESSLER 2,939,435

MARINE BOILER Filed Feb. 6, 1957 8 Sheets-Sheet 3 FIG.3-

OUTLET INVENTOR.

George W. Kessler ATTORNEY June 7, 1960 e. w. KESSLER MARINEBOILER 8Sheets-Sheet 4 Filed Feb. 6, 1957 Y INVENTOR.

I George W. Kessler ATTORNEY.

June 7, 1960 e. w. KESSLER MARINE BOILER 8 Sheets-Sheet 5 Filed Feb. 6,1957 ATTORNEY June 7, 1960 G. w. KESSLER 2,939,435

MARINE BOILER Filed Feb. 6, 1,957 8 Sheets-Sheet 6 FIG. 6

George W. Kessler ATTORNEY June 7, 1960 G. w. KESSLER 2,939,435

MARINE BOILER Filed Feb. 6, 1957 8 Sheets-Sheet 7 INVENTOR. George W.Kessler wow,

ATTORNEY MARINE BOILER 8 Sheets-Sheet. 8

Filed Feb. 6, 1957 INVENTOR. George W. Kessler ATTORNEY MARINE BOILER""slei", EWe'StB iIrY KX, "a'sfs igiirh' to The Babcock a WilcoxCompany, New Y-er'u, Nev,

'poration etNew Jersey Fir arms, 1.951, Serena-6385s! *18 Claims.c|.1'2'2==4'7s This invention relates to, a'fluid' heating apparatus'and more-particularly to an improved construction and operation of awater tube steam boiler including a novel superheater' arrangementwhichis particularly adapted for use in raemarinetinst-allation. r i

A's the'trend in marine installations is toward higher optimum superheatsteamdemperature, it has been noted that in connection with thegeneration of high pressure and temperature steam in marine boilersfired by residual oiltype fuels, serious difficulties have beenencountered in maintaining metal temperatures of the superheater partsbelow the high temperature corrosion limits thereof,

he; 'the temperature' at-which corrosion becomes excessive,

when-the same are customarily subjected to the high temperature-'combnstion gases for producing desired relatively very hightemperature 'superh'eat steam. It has been discovered that the corrosiveimpurities present in the residual fuel oils fired react'with the metalsuper produced while maintaining the metal temperatures of thesuperheater parts at or below their high temperat e corrosion limit.

Heretofor'e, control superhe'at temperature overa wide range in a marineinstallation has been attained by means of a two-furnace, single uptake,control superheat boiler. As marine steam generating installations ofthis type are characterized by relatively'low spaceand head room limi-'tatio'ns, it is a necessary requisite that these units be com} pact andlightweight in design, yet capable of adequately high thermal efiiciencyrequiring the minimum alteration of the surrounding ship structure.Because of the initial limitation ofavailable installation space, unitsof this type were limited to the amount of steam superheating surfacescapable of being located therein in a position for effective heatabsorption, the limited amount of superheater absorption-surface beinganother factor which advers'ely' affects the desirability of maximumsuperheat temperaturewith'optimum permissible metal temperature ofthe'supe'rheater parts; i

It is another object 'oflthis' invention to provide in a marine boilerunitofa predete'r'minate weight and size,

means for providing maximum. superheater absorption 'surfaceswithoutmaterially altering'or enlarging the' acceptableor allowablesizea'ndweight of the marine-boiler which must of necessity be limited tothesurroundin'gl ship structure in which his to be'in'stalled. a r

It is anotherobje'ct or this invention to provide animp'rove'dsuperheater arrangement capable ofgreaters'efiec- 2,939,435 PatentedJune 7, 1960 tiveness, yet is rendered readily accessible and easilymaintained so that the same can be sustained over a relamay long periodof time. V V

The above objects and advantages of the instant invention are attainedby providing in a marine boiler burning residual fuel oils, an improvedsuperheater construction comprising of atleast-a pair of superheatersections which are serially connected whereby each section thereof isdisposed in adjacent progressively'decreasing gas temper- .aturenones ofagas convection pass. According to this invention, each section consistsof a pair of verticaljuxtaposed headers of which at :leas t one isprovided with means forpartitioningthe same into distinct chambers and aplurality of horizontally etxending, nested U-shaped, superheatertub esconnecting the charnbers of one header in communication withitsassociated header. With this arrangement, each section is providedwith a plurality of steam passes serially connected which are generallyin counter and parallelheat transfer relationship to gas flow throughthe convection pass and which through any crosssectional plan or sectionof the entire superheater is provided with a stearri passwhich is inboth counter and parallel heat transfer relationshipto the gas flow. V

In one form of the invention, each section of the, superheaterisconnected in series. by airelatively large diameter crossover tube andin another forrn of the invention, each sectionis connectedinseries bya-plurality of additional ush d s e h at t v With eitheriofthesejarrangements, the relatively cool saturated steam accumulated thesteam drum is first introduced into that .sectionof the superheaterdisposed in the hotportion of the gas convection zone. This relativelycool steam is then-passed through the first section serially-in severalalternating passes which are generally in acounter and. parallel heattransfer relat-ionship tothe gas flow whereby the steam is heated to anintermediate superheat' steam temperature. Theintermedia'te superheatedsteam is then introduced into the second or next succeedingsuperheatersection which is: disposed in the relatively cooler portion of theg'aspass whereby the intermediate" superheatedsteam is againsuccessively or serially passed in; several alternating passes which aregenerally in counter and parallel heat transfer relationship relative tothe gas flow so as to become highly superheated thereby. .In-thismanner, efiective heat transfer isattained to produce the desired hightemperature superheat steam while at the same time maintaining the tubetemperatures of the various parts of the super-heater below thattemperature at which corrosion becomes excessive.

V According to this invention, the superheater cavity is also extendedto a extent without materially increasing the weight and size of theboiler as determined by the surrounding ships structure. This isattained by boundingthe superheater cavity by a group of spaced screentubes which are connected to a pair .of spaced relatively small diameterwater headers or drums rather than to'a single relatively large waterdrum as was heretofore customary in a comparable boiler arrangement asshown in the patent to Rooney 2,332,534. .With this novel arrangement,the' superheater cavity may extend downwardly an amount suilicient'tofacilitate the addition of several more superheater tubes, therebyincreasing the amount of available superheating surface over those ofrior known-eenstructien havin the same vertical height between upperermn and lowert'ubeheade r. i

Thisd'ual header arrangement is of further advantage in' that by spacingthe same, a hopper-like bottom is provided for the superheater cavity'whereby the superheater tubes can be readily washed" down and otherwisemaintained; thereby facilitating cleaning ofthe super- ;heat'er partsandconsequently' rendering the same more simple .in construction,

provision whereby highoptinium superheat steam tem-.

peratures are attainable while maintaining the metal temperature of thesuperheater parts within trouble-free temperature i A still furtherfeature of this invention resides in-the provision whereby thesuperheater parts can be readily cleaned and washed down as required. Y

Other features and advantages will be readily apparent when consideredin view of the following description and drawings in which:

Fig. 1 is a partly diagrammatic sectional elevation view of animprovedmarine boiler installation in'accordance with the instantinvention. j

Fig. 2 is a plan section taken along line 2-2 of Fig. 1. Fig. 3 is afragmentary, enlarged detail, elevation view of the improved superheaterarrangement according to this invention. V i

Fig. 4 is a partly diagrammatic section in elevation of a modified formof the'invention;

Fig. 5 is a plan section'taken along line 5-5 of 'Fig. 4. Fig. 6 is afragment y, nlargeddetail view of a modified superheater arrangementshown by Fig. 4.

Fig. 7 is a diagrammatic not to' scale perspective view of thesuperheater arrangement of Fig. 3.

Fig. 8 is a perspective not to-scale schematic view of the superheaterarrangement 'o'f'Fig. 6.

In the form of the invention illustrated in Figs. 1 to 3, the improvedmarine boiler of this invention consists of a setting 10 comprising of afront 11, rear 12, and side walls 13 and 14 which are substantiallyrectangularly disposed enclosing a main furnace cavity 15, an auxiliaryfurnace cavity 16 and a gas convection pass 17 associated with thelatter and disposed, between the auxiliary and supported the steam andwater drum 18. Laterally offset and disposed adjacent the lower portionof the side wall 13 is a water drum 19 which is connected to the steamdrum 18 by a bank of inclined steam generating tubes 20 which extendlongitudinally of the drums 18 and 19 and transversely across thesetting. On the outer side of the generating tube bank 20, the side wall13 connects to the front and rear wall to form a common flue 21 forexhausting the combustion gases of both furnaces, the gases of theauxiliary furnace 16 flowing through the convection pass 17 across themain furnace to the flue. Immediately adjacent the inner side of thetube bank 20 is located the main furnace cavity which is adapted to befired by fuel burners 22. If desired, a heat trap in the form ofeconomizer tubes and/or air heater tubes 23 are advantageously locatedin the flue 21.

The auxiliary furnace 16 is separated from the main furnace 15 by theassociated gas convection pass 17. As shown the side 16a, roof 16b andrear wall 16c of the auxiliary furnace cavity are lined withwater-cooled wall tubes. The sidewall'water tubes 24'extend verticallyfrom the lower side wall header 25 and the extensions thereof are,angularly inclined adjacent the roof to continue along the same toconnect with the water and steam drum 18. The rear wall tubes 26 extendbetween the 4 34 located in the front wall independently fire theauxiliary furnace.

A distinctive feature of the instant invention resides in the provisionof a pair of spaced relatively small water drums or headers 30 and 31which extend transversely across the setting adjacent the bottom of thegas convection pass. Connecting each of the headers 30 and 31 to thesteam and water drum 18 are a spaced group of water tubes 32 and 33which extend transversely of the setting and form therebetween asuperheater cavity, the tubes 32 and 33 forming a water cooled screenfor protecting an improved superheater 35, as will be hereinafterdescribed, disposed within the cavity from excessive radiantlytransmitted heat from high temperature gases in furnaces 15 and 16.

In the embodiment of Figs. 1 to 3, the screen tubes 32 extend upwardlyfrom the water header 30 and incline slightly toward the main furnace15,'the lower half'por- 'tion of the screen tubes 32 comprising a shieldof bare, tangent touching tubes to protect the superheater- 35 fr'omflame radiation. Alternate tubes 32 at the upper half portion thereofare bent inwardly toward the superheater cavity to 'form' spacestherebetween to provide passage openings for the combustion .gasesflowing through the gas convection pass.

include a pluralityof downcomers disposed between the outer casing 36and walls 11 and 12 of the'setting 10.

Referring to Figs. 1 and 2, drum 18.is connected to water drum 19 bydowncomers 37. Downcomers 38 and 39 connectthe drum 18 to the spacedwater headers 30 and 3L-respectively. Downcomer 40 connects the drum 18to the rear wall header 27 and downcomer 41 connects the drum 18 to sidewall header 25. The space formed by the walls 11 and 12 and casing 36further provides a chamber through which combustion air is supplied tothe burners 22 and 34.

. According to this invention, the improved superheater arrangement 35has its heat absorbing surfaces positioned in the gas convection pass 17whereby said surfaces can be independently heated by the firing of theburners 34 associated with the auxiliary furnace cavity and therebyrendering superheat steam temperatures controllable over a relativelywide range. Since the trend in marine boilers is toward higher superheatsteam temperatures, it has been discovered that because of the corrosiveimpurities present in the residual fuel oils, the superheater tubes.rapidly corrode or deteriorate if heated to temperatures above 1150 F.Consequently for all practical purposes,

the temperature of superheat steam obtainable is limited perature zonesA and B of the gas convection pass 17.

In the illustrated form of the invention, reference being hadparticularly to. Figs. 3 and 7'; the superheater 35' is lower and upperrear wall headers 27 and 28 respectively, v,

shown as comprising 'an inlet section 42 to' an outlet section 43. Theinlet section 42 includes a pairof vertically disposed juxtaposedheaders '45, 46 positioned between thecasin-g 36' and adjacent the 'rearwall 12,,one -of thegheaders having connectedtheretoa steam, inlet ,pipe44 connecting with .the steam drum 1-8, and the :outlet .section.consistingof juxtaposed headers 51 and 52, header 51 being providedwith an outlet connection 58 for delivering the .finally superheatedsteam to a .point of use (:not shown).

As shown, header 45 is divided by a diaphragm 47 which partitions header45 into anupper. inlet and alower "outlet chamber 48 and 49respectively. Chambers 48 and 49 of header 45 are connected .incommunication with the associated header-46 by a plurality of .nested,vertically spaced, U-shapedheat receiving superheater tubes .50. In theillustrated form of the invention of "Fig. 3, the superheater tubes 5.0are vertically stacked .in nested groups of three, the verticallystacked tubes 50 being divided into an upper group 50A connecting the.upper header chamber 48 to the associated intermediate header and-alower group 50B connecting the associated header 46 to the lowerchamber149 .of header 45.

Referring to Fig. '2, ;it will .be noted thatthenested, verticallystacked .tubes of .group 50A each comprises an inlet leg portion 50Aextendinghorizontally across the convectionpass, a .cross-o'venportion.50A forming a continuation thereof which extends beyond the front wallof the unit and a return leg .50A which also extends across theconvection ;pass upstream of the gas flow from that of the intake legportion 5 A Each of the .nested and vertically stacked group of tubes50B likewise comprises an =intake.leg portion 0B in communication withthe interior of header 46 and which extends -horizontally across theconvection pass, a crossover por-- tion 508 forming a continuation ofleg503 extending through the front refractory .wall and return leg portion50B spaced downstream of intake leg portion 5.0B

.leg 50B being in communication with chamber 49. In .Figs. 3 .and;7,.itwill.be noted by the broken-arrowindicating the steam flow that thesaturated steam from the steam dru-m'is introduced into header 45through inlet 44 and flows through the inlet section 42in the followingmanner. The-steamintroduced into header 45 flows into chamber 48, thenthrough the intake leg portion 50A, ofnestedtubetgroup 50A, through thecross-over portion 50A; .and through the return leg portion :50A whereinthe steam is discharged into the associate header 46 .in-a steam flowpath which is generally in a counterflow, heat transfer relationship tothat of thevgas flow. The com- .bined delivery of steamfrom all of thetubes 50A then .moves down the associate header-46 and .into the lowergroup of superheater tubes 50B whereby the steam is directed from header46 through .the intake leg portion 50B through the cross-over portion503 thence through the return leg portion 5013 andfinally into lowerheader 52, the header 51 being divided by a diaphragm :53 into upper andlowercharnbers 54 and 55 respectively.

Vertical stacks o'fnested U-shape heat absorbing tubes 56 connect thechambers 54 and 55, header 51 to its associated header, the stack oftubes 56 being divided into a lower portion 56A connecting the lowerchamber 55 to the associated header 52 and an upper group 563 connectingthe associated header 52 to the upper chamber 54'.

. Referring to Fig. 7, each of the nested tubes vertical- 56Ajcomrnunicating with chamber 55 and extending 'tion 56A form-ing acontinuation of leg 56Aywhi'cli extends through the frontre'fractory'wall 1-1 and a return 1y stacked in group 56A comprises "anintake leg portion:

across zone Bot the convectionpaiss, a cross-over porassets;

.leg .portion 56A spaced upstream of the intake leg ,portion 562. withrespect to thefgas flow, 'the return 'leg portion '56A being incommunication with the interior of theassociatedintermediate header'SZ.Thus, it will he noted that the intermediate superheated steamintroduced into chamber '55 through the cross-over tube 57 Iilowsthrough the intake leg portions 56A of the tube group 50A through thecross-over portion 56A and ithencethrough the return leg portion 56A;wherein the .steam is discharged into the associated header 52, thesteam traversing allow path through tubes 56A which is generally inacounterflow heat transfer relationship Eto that of the gas 'flowfin theconvection pass. The combined delivery of the steam from all of thetubes 156A then moves .up the associated header'SZ and flows outwardlytherefrom through'the inta'ke leg portion 56B, through the cross-overportion 56B: forming'a continuation thereof and thence through theretur'ri leg' portion -56B .spaced downstream of leg portion 56B withrespect to gasfiow wherein the steam is finally discharged .into theupper chamber "54 ofheader 51, the steam traversing .a flow ,paththrough tubes 56B which .is' generally in a parallel heat transferrelationship to that of the gasflow. Thus, it wiIl be noted that'theintermediate .superheat steam flowing through the outlet section 43 ofthe superheateruis raised to its finally superheated steamtemperaturelinwhic'h state it is delivered through the 1 outlet pipe 58at fits optimu'm' superheated tempera- .turetto a point of use. p

. -By this arrangement, it will be noted that the relative cool steam atsaturated temperature is first intro- .duced .into section '42 of thesuperheater, the heat ab- :sorptiomsurfaces of which .are exposed to thehottest gas in zone A in the gas convection pass, and that by flowingthesteam serially inseveral alternating counter and parallel flow heattransfer \relationshhips between header 45 and 46 in the hotzone, thesaturated steam is superheated to an intermediate temperature wherebythe relative steam temperatures within the tubes 50 and thegastemperature heating the surfaces thereof are such that thesuperheatermetal temperatures are maintained below their hightemperature corrosive limit. The intermediate superheated steam is thenpassed into the second section ofthesuperheater, disposed in the coolerzone Band the steam finally heated therein by means of flowing the steam.in through the second superheater section in ,generally an alternatecounter and parallel heat transfer relationship to the gas flow. Thus, ahighly heated 'superheat steam is attained in that portion ofthesuperheater having its metal .heat absorption surfaces exposed to therelatively cooler combustion gases of zone B. In this manner, a moreuniform balance is achieved between therelative temperatures of thesteam, the combustion gases and theassociated metal superheaterparts incontact therewith. Consequently, this balance is maintained so that theoptimum superheat steam temperatures of 1000 F. or above may be achievedwithout ,the metal parts of the superheater parts exceeding temperaturesat which intolerable corrosion of the superheater tubes 50 and 56occurs. 7

According, to this invention, it will be 'noted that the utilization ofthe spaced water header construction 30 and 31-as hereinbefore describedenables the superheater 'cavityor section to' be extended downwardly amaximum extent. This 'is rendered possible over the priorknownconstruction because it has been discovered that by utilizing a pair ofspaced smaller diameter water headers 30' and 31, the tube groups 32, 33connecting into each of the water headers '30 and 31 respectively.klower ends thereof 32a, 33a.are bent for connecting the .same into itsrespective header. For this reason; additional-space is availed ofwithout altering the overall size of .the'unit whereinseveral additionalsuperheater tubes '50 and 56 may beaccommodated' and-thereby Itmay'extend downwardly a greater-amount before'the 'superheat steamtemperature.

, spams v '7 creasing the overall amount of heat absorbing surface ofthe superheater.- Thus it will be noted that" for a given steamtemperature withfthe greater the amount of superheater absorptionsurface available, lower resultant tube temperatures are attained andconversely,

for any .given tube temperature, the more superheater which is' adaptedto be closed by a removable closure 61.

Because of this construction, the superheater tubes 50 and 56 may bereadily washed down or otherwise maintained so that they can be keptcomparatively clean thereby increasing the efiiciency thereof. As shownin Fig. 2, the U-shaped, vertically stackedisuperheater tubes 50 and 56,nested in groups of three are rendered readily accessible in that thespace between the horizontally extending leg portions of theU -shapedtubes of each section 42, 43 provide sufficient walk-in area so that anoperator may physically enter and physically clean tubes by hose and/orscraping or. the like to maintain the tubes reasonably clean forsustaining the effectiveness of the same. Thus, the instantsupcrheater'arrangement herein described allowsfor optimum superheatsteam temperatures while maintaining the metal temperatures thereofwithin safe operating limits and also the arrangernent thereof is suchthat greater accessibility and ease of maintenance may be had-withoutincreasing or altering substantially the overall size and dimensions ofthe unit. I

It will be further noted that the tubes 50 and 56 extend through thefront and rear walls and are supported thereby. If desired, a pluralityof large diameter water tubes 62 connecting the drum 18 to headers 30and 31 are disposed in pairs adjacent tubes 50 and 56 for supporting theintermediate portion of the horizontal legs of the nested tubes, eachpair of tubes having secured thereto suitable superheater supportingplates 63.

A modified form of the invention is illustrated in Figs. 4 to 8. In thisform of the invention the marine boiler unit is arranged generally inmuch the same manner as hereinbefore described, but utilizing a modifiedsuperheater arrangement. As shown the setting 110 comprises a front wall111, rear wall 112, and side walls 113 and 114 which are rectangularlydisposed and enclose a main furnace cavity 115, an auxiliary furnacecavity 116 and a gas convection pass 117 disposed the'rebetween, each ofthe furnace cavities 115 and 116 being independently fired by fuelburner means 118 and 119. The water and steam drum 120 is supportedadjacent the upper portion of the unit and extends transversely of thesetting in the vicinity'of the gas pass. Laterally offset and adjacentthe bottom portion of the side wall 113, there is positioned a waterdrum 121 which is connected to the steam drum 120 by a bank of inclinedgenerating tubes 122. As hereinbeforc described, on the outer side ofthe tube bank I The auxiliary furnace 116 in this form of the invention.

is likewise provided with water cooled side walls 116a, rear wall 116b,and roof 1160, the side wall tubes 125 extending vertically from thelower side wall header 126 and inclining adjacent the roof of thefurnace to con- 8 tween the lower 128 and the upper 129 rear wallheaders, the latter being connected to the main steamdrum 120 by risertubes 130.

Positioned belowthe main water and steam drum 120 are a. pair of spacedrelatively small diameter water headers 131 and 132 which extendtransversely across the settingat the bottom of the gas convection pass117, each of the water headers 131 and 132 being connected to the steamdrum 120 by a group of spaced water tubes 133 and 134 respectively whichextend transversely across the setting and form therebetween asuperheater cavity.

,As hereinbefore described, the spaced group of tubes 133, ,134 form awater cooled screen for protecting the modified superheaterr135 in thesuperheater cavity from flame radiation.

As shown in Fig. 4, the screen tubes 133 extend upwardly from the waterdrum 131, the lower portion of the screen consisting of bare, tangenttouching tubes to form'an imperforate shield, while the upper portion ofthe screen has alternate tubes inclined outwardly to provide spacestherebetween for permitting the gases to flow out from the gas pass andinto the upper portion of the main furnace from whence they areexhausted through the flue 123. Screen tubes 134 are alternatelystaggered throughout the greater portion thereof. Thus, it will be notedthat when the burners of the auxiliary furnace are "fired, thecombustion gases tend to flow from the auxiliary furnace through screentubes 134 and into the gas convection pass 117 whereby the gases aredirected over the superheater after which the gas flows outwardlythrough the passages formed between tubes 133 at the upper portion ofthe screen.

The water supply connection from the drum 120 to the various drums andheaders of the unit include a plurality of downcomers which are disposedin the spaces formed between the outer casing 136 and the front and rearwall of the setting. Referring to Fig. 5 downcomers 137 connect the drum120 to the water drum 12 1 and downcomers 138 and 139 connect the steamdrum to the spaced water header 131 and 132 respectively whiledowncomers 140 connect the steam drum 120 to the side wall header 126and downcomer 141 connects the steam drum to the rear wall header 128.

The modified superheater arrangement 135 as illustrated in theembodiment of Figs. 4 to 6 and 8 comprisesan inlet section 142 and anoutlet section 143. As shown in Fig. 6, the inlet section 142 includesan inlet header 144 and a juxtaposed associated header 145 verticallydisposed between the casing 136 and the rear wall 112, each header beingprovided with a diaphragm means 146, 147, respectively for partitioningeach into an upper and lower chamber. As shown in Figs. 6 and 8 it willbe notedthat the diaphragm 146, 147, dividing their respective headersinto upper and lower chambers, are

' located at different elevations whereby the inlet header drum 120. Therear furnace wall tubes 127 extend be- 144 is divided into an upperchamber 148 and a relatively shorter lower chamber 149 while theassociated header is divided so as to have substantially equal lower andupper chambers 150 and 151 respectively which are approximately doublethe length of the lower inlet header chamber 149.

A group of horizontally, vertically stacked, nested,

hairpin tubes 152 extending through the rear wall and across the hotzone of the gas pass connect the chambers 148 and 149 of the inletheader 144 with the chambers 150 and 151 of the header 145. As indicatedin Fig. 6, the vertically stacked, hairpin tubes 152 are divided into anupper portion 152a, an intermediate portion 152b, and a lower portion1520. The lower portion 152:: of

V the tubes 152 connects the lower chamber 149 of the inlet header 144to the lower half of chamber 150, the

f intermediate group 152b connects the upper half of chamber l'50 ofthe-associated header 45 with the lower portiorrof the upper inletheader chamber 148 and the upper group of tubes 152a connects the upperportion of the :and extending across the cooler portion gaspass'connects the chambers-157, 158 of the outlet header-153 With'thesehambers 159, 169 of the associated header 154, the verti- 1calstack oftubes 161 being divided into an -upper161a, intermediate 161i) and lower161c portions. 1 Referring to Figs..6, and ;8 ,it will'be noted that-theupper portion .1611: of thetubes, 161;connects. the upper chamber 159 ofThe outlet section 143 includes an outlet-header 153 ,and a juxtaposedassociated header 154 vertically disg'pOSQd between the casing 136 andthe rear wall .and spaced from inlet section v142.. .T-he headersj153and 154 of the outlet section 143 are likewisepartitioned by means of,diaphragms 155, .156 wherein-the diaphragm divides the outletheader153-into upper and lower chamqbersl57, 158,'respectively, which-aresubstantially equal {and correspond inlength to,therespectivechambers148 ;-and 149 of the. inlet header 144: and v the associated header 154is divided into upper and lower chambers 159-160 ,substantiallysimilarto that of the *associatedhea'der .145 of the inlet section.

vA group of horizontallyextending verticallysta'cked hairpintubes 161extending throughthe rear Wall 112 associate header :154 to the-upperportion of the upper chamber; 157 of the outlet header. .Theintermediate pors,tion;161b:ofgtheitubes ccnnectsthe lower portion-of.,.the mpper chamber157 i in connnunicationwiththe upper portion f:the lower; chamber 160 of the associated, header .:1'5,4.:and Y thebottom-portion161's of the tubes connect the lower portion of thelowerchamberlfifiincommuni cation with the.lower chamber :158 of theoutlet header .1153. Thus it will be noted that the steam flowsthrough.lthesuperheater outlet section 143 in a plurality of. passes .inalternating parallel and countersteam flow heat trans- :fcrrelationshiprelative to the gas flow through the convcction pass.

According to this form of theinvention, the superheater inlet section142 ,and outlet section 143 are con- :nected in series by means of aplurality of horizontally =.extending, vertically stacked, nestedtpairsof U-shaped, -crossover tubes 162 which extend across the convect on gaspass, the U-tubes connecting the upper chamber 151 of the header 145 tothe upper chamber 159 of the header 154. In addition to the functioningas cross-over tubes,

'the group of U-shaped tubes 162 also increase the amount z-available ofheat absorption surfaces of the superheater. :It will be further notedthat the vertically arranged tubes 1610f the outlet sectionarenested inpairs. .velocity of the superheat steam in the outletsection isincreased thereby functioning as an aid to maintain lower Thus the tubetemperatures in that portion of the superheater in which'the'highersteam temperatures are attained.

In the modified form of the zsuperheater relatively co'ol saturatedsteam is introduced into the inlet section JIM-which is disposed in thehot zone A of the convec- ;tion pass 117 through pipe 163. Flowing thesteam back and'forthbetween the headers144 and 1 35 of the inlet sectionthrough-tubes 152 in alternate passes of parallel and counter flow heattransfer relationship, as indicated Tby the arrows, the'saturated steamis etiectiv ely superheated to an intermediate temperature.

ate superheat steam is. then directed into the outlet seclliOn 142through thecross-over superheater tubes 162,

The intermedi- =whereby the steam is iinallysuperheatedto maximum:temperatures by passing the same through a series of :parallel andcounter-fiow heat.transfenrelationship bef tween headers 153 andl54'through tubes "161, the latter being disposed: in thetcooler;-.-por.tio n .B'- -ofs. the -gas;;pat's.

' Thus, the ;.arrangement;1is such ;that the hottest esteam temperatureis attained in that portion of the superheater disposed in :the coolestportion oof the gas t convection :5 apass, ithe zarrangement 'being suchthat maximum steam -itemperatures are attained while maintainingtubetem-,iperatureubelow theinh'igh temperature corrosive limit. ,Thezfinallyzsuperheated steam is then discharged through :pipe'16 4. l

As :hereinbefore, described,; two spaced water headers 1131 and 132enable the superheatercavity to extend downwardly-amaximum-extent. Inaddition, the conustmctionturther enables 1the=superheater cavity .to beeprovidedewith-a hopper-like bottom 165having an open-.15.ing;166;-disposed-;between the. headers 131 and 132,.the

opening 1166 :being provided' withta'. suitable closure 167. .Thus,.withathiseconstruction, maintaining and cleaning eat .the :tubes isz-greatly :facilitated as hereinbefore .de- :scribed. 1

In both forms of the invention illustrated, it will be:n'oted;that?.the:.-superheater tubes:50, '56, 152, 161rand 1'62:exten'd ,through: both the refractory front and rear walls. and;arexsupported. thereby, thus, greatly facilitating .andcsimplifyingathefabrication .and supporting means of ,1125 c-theasuperheater tubes.

.The operation-of-..-the boiler I .:scribedis as?follows:

..The:stearn generatingunit is started up with only the main furnaceburners in use. Thenheating gasesgener- :atedlbythe-"fuelz'burninginssuspension in the main fursnac'e flow {transversely-of fthegenerating tube bank to ;-thegas:-ontlet :flue, passing .over the airheater and/or neconomizertubes ,before leaving the unit, the water-.cooled screen' tubes forming :an effective radiantheat shield betweenthe main .furnace cavity and the superheater. tubes. When: sufficientsteam: is flowing .through :the isuperheater. tubes, theuauxiliaryfurnace burn'ers are :startedup andare regulablyxoperated as tonumber'and firing :rate to control the :superheat steam temperatures. Theheating gases generated in the auxiliary furnace :ehambers flowsubstantially'horizontally across'the rows of screen tubes and.superheater-tubes throughout .their {length due to the :gasflow:equalization space formed by the arrangement of the screen tubesthroughoutits extent in space relation 'withI-thesuperheater tubes. Thisconstruction further facilitates efiective convection .:heating of 'theentire isuperheating surface.

According to this invention the hottest gasesgenerated in the auxiliaryfurnace cavity flow through the rows-of 'staggeredscreen'tubes 33, 134and across the superheater tubes '50, 1'52, thelatter thus beingdisposed in the hot-test portion of the gas convection pass. Flowingthesteam in a plurality of passes that are in substantial parallel andcounter flow heat transfer to the gas flowing over tubes50, 152 of theinlet section of the superheaL- efiectively superheats thestearn thereinto an intermediate temperature whereby hot combustion gas temperaturesin contact therewith are proportionately cooled. Thus the'tubessubjected to the hottest 'gases are in contact with relative lowtemperature steam.

The intermediate superheat steam is then directed to vthe outlet sectionof the superheater. The relatively cooler combustiongases flowing oversections 42, 142 are then brought into contact with the outlet section43, 143 of'the superheater wherein the intermediate superheat steamflowing through the outlet section in a'plurality of passes ofalternating counter and parallel 'flo'w heat transfer relative to thecombustion gas flow becomes highly superheated therein. Thus, it Will benoted that 70 the tubes exposed to the higher steam temperature'areexternallyin contact with the lowergas temperatures in the gas pass.Consequently the arrangement is such that the balance of relativetemperatures attainablebetween the combustion gases, metal parts of the--super- 75 heater 7 and steam in contact therewith enables theattainarrangements herein de- "ment of maximum temperature of superheatsteam without exceeding safe operating superheater tube temperature. a

After leaving the superheater tubes, the gases flow across the upperportion of screen tubes 32, 133 and through the passage opening thereofto the extreme upper portion of the main furnace cavity. Theconfinementof the auxiliary furnace products of combustion to the extreme upperportion of the main furnace cavity avoids the introduction of relativelycold and inert gases into the main combustion zone of the main furnacecavity so that combustion is completed therein with little or nointerference by the heating gases'of the auxiliary furnace. 'The gasesare then passed across the upper end of the tube bank to the outlet fluewithin which they contact the economizer and/or air heater tubes. Thecontact of these gases with the bank of tubes and air heater oreconomizer tubes further reduces their temperaturesto the desired value,thereby increasing the efficiency of the unit.

The fuel supply to the burners in either of the cavities can beregulated either manually or automatically to maintain any desiredsuperheat temperatures over a relatively wide range. The describedconstructions are particularly advantageous in providing a heating gasflow path from the auxiliary furnace chamber which follows the naturalflow path of the gases without any substantial change of direction ofthe same; consequently the. pressure .drop throughout is extremely low.I

From the foregoing description it will be noted that the two furnace,single uptake type, marine boiler of the instant invention is providedwith a superheater having more heat absorptionarea effectivelydisposed'in a gas convection pass which is divided into progressivelydecreasing temperature zones wherein steam is effectively superheated instages from a saturated steam temperature to an intermediate superheattemperature in the hot zone and from said intermediate temperature to ahigh optimum superheat temperature in the cooler zone. This isaccomplished by flowing the steam in each zone in a plurality ofalternating parallel and counter-flow steam heat transfer relationshiprelative to the gas flow through the convection pass. Thus the heatingof the relatively cool saturated steam to an intermediate superheattemperature in the hot zone and highly superheating the intermediatelyheated superheat steam in the cooler zone as described provides theattainment of maximum superheat steam while maintaining superheater tubetemperatures within their high temperature corrosion limit.

Further, the arrangement is such that superheater cavity is bottomed bya pair of space water headers to provide for the formation of a hopperbottom having a centrally disposed opening to facilitate maintenance,hosing and cleaning of the superheater tubes. Also the nesting of thesuperheater tubes into relative small groups further aids in renderingeach tube individually accessible for cleaning.

While the instant invention is disclosed herein with 'particularreferences to specific embodiments thereof, it is to be appreciated thatthe invention is not to be taken as limited to all of the detailsthereof, as modifications and variations thereof may be made withoutdeparting from the spirit or scope of the invention.

a What is claimed is:

1. In combination with a two furnace, single uptake, controlledsuperheat boiler, the improvement of a gas convection pass disposedbetween said furnaces, said pass having progressively decreasing gastemperature zones, asuperheater arrangement having a pluralityofsections serially connected and including a first section disposed inthe hottest gas zone and each succeeding section being located insuccessive lower temperature zones of said gas pass, said sections eachincluding a pluralityof heat aborbing superheater tubes extendingtransversely of its .respe tive temperature zone, means for introducingsaturated steam into said first section and means for serially flowingsteam through each of said sections successively in a steam flow that isin an alternating counter and parallel flow heat transfer relationshipto the gas flow whereby said steam is superheated in each section tosuecessive increasing superheat temperature until said steam issuperheated to an optimum high temperature, said high temperatures beingreadily available while said tube temperatures are maintained withintolerable corrosive temperature limits.

2. The invention as defined in claim 1 wherein a said steam flow throughsaid superheater in a plan section thereof is in both counter andparallel flow heat transfer relationship to said gas flow.

3. In combination with a two furnace, single uptake, controlledsuperheat boiler, the improvement of a gas convection pass disposedbetween said furnaces, said pass having progressively decreasing gastemperature zones, 'a superheater arrangement including a first sectionand a second section serially connected, each section being located insucceeding temperature zones of said gas pass, said sections eachincluding a plurality of heat absorbing superheater tubes extendingtransversely across its respective temperature zone and means forserially flowing steam through each of said sections in a steam flowthat is in an alternating counter and parallel flow heat transferrelationship to the gas flow whereby said steam is superheated in eachsection to successive increasing superheat temperature until said steamis superheated to an optimum high temperature, said high temperaturesbeing readily available while said tube temperatures are maintainedwithin tolerable corrosive temperature limits.

4. In combination with a twofurnace, single uptake, controlled superheatboiler, the improvement of a gas convection pass disposed between saidfurnaces, said pass having progressively decreasing gas temperaturezones,

a superheater arrangement including a first section and a second sectionserially connected, each section being located in succeeding temperaturezones of said gas pass, said sections each including a plurality ofvertically disposed heat absorbing superheater tubes extendinghorizontally across its respective temperature zone and means forserially flowing steam through each of said sections in a steam flowthat is in an alternating counter and parallel flow heat transferrelationship to the gas flow whereby said steam is superheated in eachsection to successive increasing superheat temperature until said steamis superheated to an optimum high temperature, said high temperaturesbeing readily available while said tube temperatures are maintainedwithin tolerable corrosive temperature limits.

5. In combination with a two furnace, single uptake, controlledsuperheat boiler, the improvement of a gas convection pass disposedbetween said furnaces, said pass having progressively decreasing gastemperature zones, a superheater arrangement including a first section,said first section having a plurality of heat absorbing superheatertubes extending transversely of said convection pass in the hottest zonethereof, means for serially flowing relative cool, saturated steamthrough said tubes in a plurality of passes in alternating counter andparallel flow heat transfer relationship to the gas flow whereby saidsteam is heated to an intermediate superheat temperature, a secondsection, means connecting said sections in series, said second sectionincluding a plurality of superheater tube members extending transverselyof the convection pass in the next succeeding lower gas zone, and meansfor serially flowing said intermediately heated steams through said tubemembers in a plurality of passes in alternating counter and parallelfiow heat transfer relationships to the gas flow whereby saidintermediate steam is superheated to an optimum high temperature wherebysaid high steam temperature is obtainable while superheater tubetemperatures are kept within tolerable corrosive temperature limits.

:6. A;marine boiler consisting of -a-setting, tanwupper steam and waterdrum, a laterally offset lower, water drum, a bank of inclinedsteamgenerating-tubes connectinggsaid upper and lower drums, a pair ofspaced water headers arranged below said upper drum, spaced groups ofvertically arranged water tubes connecting the upper drum to each ofsaidlower pair of water jheader-s, said spaced groups oftubes formingtherebetween a superheating cavity and said pair of spacedwaterheaderscooperating to extend the superheater cavity to a maximumextent and toform ahopper bottom of said superheater .cavitytofacilitate cleaning of the same, a main furnace chamber between saidtube bank and said tube group, means for firing said mainfurnace, amulti-steam-flow csuperheater disposed in said superheating cavity andscreened by said spaced group of water tubes for super- :heating steamto a relatively high temperature while maintaining saidsuperheatertemperature below its high tternperature'corrosionlimit, anauxiliary furnacecham- ;ber laterally adjoining .theouter side'of'saidsupcrheater tubes, means for independently firing said auxiliary furnacechamber, a singleheating gas outlet flue at the outer side .of said tubebank and arranged to receive :all of .the heating gases flowing fromboth of .said furnace chambers, said flue beingso located that the heat-:ing gases from said auxiliary furnace chamber ,tend ;to how oversaidsuperheater, through themain furnace tchamber and across said tubebank before entering --said;flue, said steam flow in said superheaterbeing in alternating counter and parallel flow heat transferrelationship with respect to the -.ga ses flowing from said auxiliaryfurnace.

' 7. Theinvention as defined in claim 16 wherein the lower :half of saidgroups of vertically arranged tubes disposed between the :main furnaceand said ,muti-pass :superheater are contiguous tangent touching tubesto :shield said superheater from'flame' radiation.

-8. A' marine boiler consisting of setting, auuppersteam and .waterdrum, a laterally offset lower water drum, 'a bank of inclined steamgenerating tubes connecting said upper and lower drums, a pair of spacewater headers .sarranged below said upper'drum, a spaced group ofveritically arranged water tubes connecting the upper drum :to each'ofsaid lower pair of :waterheaders, said spaced group oftubes'formingitherebetween a superheater cavity and said pair of spacedwater headers'cooperating'toex- 'tend the superheater to a maximumextent andto form a hopper bottom for said superheater cavity tofacilitate cleaning of the same, a main furnace chamberbetweensaidtube'bank and said tube group, means for firing said :main furnace,a series multipass-superheater disposed in said superheating cavity andscreened by said spaced group of water tubes, an auxiliary furnacechamber laterally adjoining the outer side of said'superheater'tubes,means for independently firing said auxiliary furnace chamber and asingle heating gas outlet flue at the outer side of said tube bank andarranged to receive all of the heating gases flowing from both of saidfurnace chambers, said flue being so located that the heating gases fromsaid auxiliary furnace chamber tendto flow over said superheater,through the main furnace chamber and across said tube tank beforeenteringsaidflue, said steam flow in said superheater being inalternating counter andpar- 'allel flow heat transfer relationship withrespect to the gases flowing from said auxiliary furnace.

9. A marine boiler consisting of setting; an upper .steam and waterdrum; a laterally offset lower water drum; a bank of inclined steamgenerating tubes connectingsaid upper and lower drums; a pair of spacedwater headers arranged below said upper drum; a spacedvgroup ofvertically arranged water tubes connecting the upper drum to each ofsaid lower pair of water headers, said spaced group of tubes formingtherebetween a superheater cavity and said pair of spaced waterheaders'cooperating to form a hopper-bottornfor. said .superheater its cavity tofacilitate cleaning the same; -a mainfurnae chamber between said tubebank and said tube group; :means for firing said main furnace; atsuperheatcrri cluding a pair of vertical, juxtapositioned headers, oneof :said header-s having a diaphragm means dividing the same into aplurality of chambers and plurality of vertically stacked, horizontallyextending U-shaped tubes :counecting chambers of said latter header ,tosaid other :header for establishing a criss-crossing steam flow pathbetween said headers said U-shape tubes being disposed in saidsuperheater cavity and screened by said spaced ;,g 0111) of water tubes;an auxiliary furnace chamber laterally adjoining the outer side of saidsuperheater-tubes;

auxiliaryfurnace chamber tend to, flow over said super- ,heater inalternating parallel and counter flowheat transfer relationship to'thesteam flow through said superheater, thence through the .mainfurnacechamber and .across-said tube bank before entering said flue.

10. A marine boiler comprising of a'setting having -a main furnacecavity; an auxiliary furnace cavity; a gas .convection pass associatedwith said auxiliary furnace :cavity and disposed between said furnacecavities, said convection pass including a hot gas zone and a relativelycoolergas zone; means for independentlyfiring each of said furnacecavities; an upper stream and water drum;

,a-laterally offset lower water drum; a bank of inclined steamgenerating tubes connectingsaid upper and lower .drums; a pair of spacedwater headers arrangedbelow said upper drum; a spaced group ofvertically 7 arranged water tubes connecting the upper drum to each ofsaid lower pair of water headers, said spac.ed group f tubes formingtherebetween a superheater cavity, said pair of spaced water headersenabling said superheater cavity to ,be extended a maximum extent andsaid spaced water .headers cooperating to form a hopper-bottom for said.superheater cavity to facilitate cleaning of the same, said -mainfurnace being disposed between saidtube bankand said tube group; asuperheater including a-first section and asecond section, said'firstsection having a first pair ofvertically disposed headers consisting ofan inlet header and, an associated header, said inlet header having adia phragm means dividing the same into a plurality of chambers, aplurality'of 'U-shaped horizontally extending tubesconnecting saidchambers of said inlet header withsaid associated headerfor-establishing a steam flow path between said first pair of headershaving a portiou which is-generally in counter flow heat transferrelationshipto saidgas flow and a secondserially connected portion whichis generally in a parallel heat transfer ,relationship to the gas flow,said U-shaped tubes being disposed in the hot zone of said superheatercavity whereby said ,steam flowing therethrough is superheated to anintermediate temperature; said second section including asecond pair ofvertically disposed headers including an outlet header and an associatedheader, said outlet header having a diaphragm means dividing thetsameinto a plurality of chambers, a plurality of U-shaped, horizontallyextending tubes connecting said chambers of said outlet header to saidassociated header for establishinga steam ,-flow path between saidsecond pair of headers having a portion which is generally in counterflow heat transfer relationship to said gas flow and a second seriallyconsnectedportionwhich is generallyin a parallelheat trans- :ferrelationship to the .gas flow, said latter U-shaped tubes being disposedin said cooler zone of said superheater cavity and a tubemeansconnecting said'sections so that the steam flows from said firstsuperheater section to said second section whereby the intermediatesuperheated steamse r tcdtinsai fi t-S c i i hly heated i '15 adjoiningthe hot zone of said superheater cavity so that the heating gases fromsaid auxiliary furnace tend to flow relative to the steam flow in thesuperheater whereby said steam is superheated to a relatively hightemperature while the superheater tube temperatures are maintained belowtheir high temperature corrosion limit.

11. A marine boiler comprising of a setting having a main furnacecavity; an auxiliary furnace cavity; a gas convection pass associatedwith said auxiliary furnace cavity and disposed between said furnacecavities, said convection pass including a hot gas zone and a relativelycooler gas zone; means for independently firing each of said furnacecavities; an upper stream and water drum; a laterally oflset lower waterdrum; a bank of inclined steam generating tubes connecting said upperand lower drums; a pair of smaller spaced water headers arranged belowsaid upper drum; a spaced group of vertically arranged water tubesconnecting the upper drum to each of said lower pair of water headers,said spaced group of tubes forming therebetween a superheater cavity,said pair of spaced water headers enabling said superheater cavity to beextended to a maximum extent and said spaced water headers cooperatingto form a hopperbottom for said superheater cavity to facilitatecleaning of the same, said main furnace being disposed between said tubebank and said tube group; a superheater includ- -inlet header having adiaphragm means dividing the same into an upper and lower chamber, aplurality of U-shaped horizontally extending tubes connecting said upperand lower chambers of said inlet header with said associated header forestablishing a steam path flowing from the upper chamber of said inletheader to said associated header and thence from said' associated headerto said lower chamber of said inlet header, said U-shaped tubes beingdisposed in the hot zone of said superheater cavity whereby said steamflowing therethrough is superheated to an intermediate temperature; saidsecond section including a second'pair of vertically disposed headersincluding an outlet header and an associated header, said outlet headerhaving a diaphragm means dividing the same into an upper and lowerchamber, a plurality of U-shaped, horizontally extending tubesconnecting said outlet header chambers to said associated header forestablishing a steam path flowing from said lower chamber of said outletheader to said second associated header and thence from said latterassociated header to said upper chamber ofsaid outlet header, saidlatter U-shaped tubes being disposed in said cooler zone of saidsuperheater cavity, and a relatively large diameter connecting tubeconnecting said lower inlet header chamber to said lower outlet headerchamber so that said intermediate superheated steam generated in saidfirst section flows to said second section to be highly heated therein;said auxiliary furnace being disposed adjoining the hot zone of saidsuperheater cavity so that the heating gases flowing therefrom isutilized to control the superheat of said steam.

12. A marine boiler comprising of a setting having a main furnacecavity; an auxiliary furnace cavity; a gas convection pass associatedwith said auxiliary furnace cavity and disposed between said furnacecavities, said convection pass including a hot gas zone and a cooler gaszone; means for independently firing each of said furnace cavities; anupper steam and water drum; a laterally offset lower water drum; a bankof inclined steam generating tubes connecting said upper and lowerdrums; a pair of smaller spaced water headers arranged below said'upperdrum; a spaced group of vertically arranged water tubes connecting theupper drum to each of said lower pair of water headers, said spacedgroup of tubes forming therebetween a superheater cavity, said pair ofspaced water headers enabling said superheater cavity to be extended 16to.a maximum extent and said spaced water headers cooperating to form ahopper-bottom for said superheater cavity to facilitate cleaning of thesame, said main furnace being disposed between said tube bank and saidtube group; a superheater including a first section and a secondsection, said first section having a first pair of vertically disposedheaders consisting of an inlet header and an associated header, saidinlet header having a diaphragm means dividing the same into an upperand lower chamber, a plurality of U-shaped horizontally extending tubesconnecting said upper and lower chambers of said inlet header with saidassociated header for establishing a steam path flowing from the upperchamber of said inlet header to said associated header in a counter flowheat transfer relationship to the gas flow and thence from saidassociated header to said lower chamber of said inlet header parallelflow heat transfer relationship 'to the gas flow, said U-shaped tubesbeing disposed in the hot zone of said superheater cavity whereby saidsteam flowing therethrough is superheated to an intermediatetemperature, said second section including a second pair of verticallydisposed headers'including an outlet header and an associated header,said outlet header having a diaphragm means dividing the same into anupper and lower chamber, a plurality of U-shaped, horizontally extendingtubes connecting said outlet header chambers to said associated headerfor establishing a steam path flowing from said lower chamber of saidoutlet header to said second associated header that is generally in acounterflow heat transfer relationship to the gas flow and thence fromsaid latter associated header to said upper chamber of said outletheader in a generally parallel flow heat transfer relationship to thegas flow, said latter U-shaped relative heating gas flow to steam flowis such that the steam is highly superheated while the superheater tubetemperatures are maintained below their high temperature corrosionlimit.-

13. A marine boiler consisting of a setting having a main furnacecavity; an auxiliary furnace cavity; a gas convection pass associatedwith said auxiliary cavity disposed between said furnace cavities, saidconvection pass including a hot gas zone and a relatively cooler gaszone; means for independently firing each of said furnace cavities; anupper steam and water drum; a laterally offset lower water drum; a bankof inclined steam generating tubes connecting said upper and lowerdrums; a pair of smaller spaced water headers arranged below said upperdrum; a spaced group of vertically arranged water tubes connecting theupper drum to each of said lower said'tube group; a superheaterincluding a first section and a second section, said first'sectionlhaving a first pair of vertically disposed headers consistingof an inlet header and an associated header, said headers each having adiaphragm means dividing the same into a plurality; of chambers, aplurality of U-shaped horizontally extending tubes connecting thechambers of said headers for establishing portions having alternatingparallel and counterflow'heat transfer steam flow paths between saidfirst pair of headers, said U-shaped tubes being disposed in the hotzone of said superheater cavity whereby said steam is superheatedtherein to an intermediate, temperature, and a second pair of verticallydisposed headers including an outlet header and anassociated header,said latter headers each having a diaphragm means dividing the same intoa plurality of chambers, a plurality of U- shaped, horizontallyextending tubes connecting the chambers of said last mentioned headersfor establishing serially connected alternating parallel and counterflow heat transfer steam flow paths between said second pair of headers,said latter U-shaped tubes being disposed in said cooler zone of saidsuperheater cavity, and a plurality of small diameter cross-over tubemeans connecting said first section to said second section fordirectingtsaid intermediate superheated steam flow from said firstsuperheater section to said second section whereby said intermediatesuperheated steam is highly heated' in the latter section; saidauxiliary furnace being disposed adjoining the hot zone of saidsuperheater cavity so that the heating gases flowing therefrom areutilized to control the superheat temperatures of said steam.

14. The invention as defined in claim 13 wherein said small diametercross-over tubes consist of a plurality of U-shape tubes horizontallydisposed in the convection gas pass whereby said cross-over tubesfunction as additional superheating tubes.

15. A marine boiler comprising of a setting having a main furnacecavity; an auxiliary furnace cavity; a gas convection pass associatedwith said auxiliary furnace cavity and disposed between said furnacecavities, said convection pass including a hot gas zone and a relativelycooler gas zone; means for independently firing each of said furnacecavities; an upper steam and water drum; a laterally offset lower waterdrum; a bank of inclined steam generating tubes connecting said upperand lower drums; a pair of smaller spaced water headers arranged belowsaid upper drum; a spaced group of vertically arranged water tubesconnecting the upper drum to each of said lower pair of water headers,said spaced group of tubes forming therebetween a superheater cavity,said pair of spaced water headers enabling said superheater cavity to beextended to a maximum extent and said spaced water headers cooperatingto form a hopperbottom for said superheater cavity to facilitatecleaning of the same, said main furnace being disposed between said tubebank and said tube group; a superheater including a first section and asecond section, said first section having a first pair of juxtaposedvertically disposed headers consisting of an inlet header and anassociated header, said headers each having a diaphragm means dividingthe same into an upper and lower chamber, a plurality of U-shapedhorizontally extending tubes connecting said upper and lower chambers ofsaid headers for establishing a serially connected alternating paralleland counter flow heat transfer steam path relative to said gas flow,said steam flowing from the lower chamber of said inlet header to thelower chamber of said associated header, thence from said lower chamberof the associated header to said upper chamber of said inlet header andthen from said upper chamber of inlet header to the upper chamber ofsaid associated header, said U-shaped tubes being disposed in the hotzone of said superheater cavity whereby said steam 'fiowing therethroughis superheated to an intermediate temperature, said second sectionincluding a second pair of juxtaposed vertically disposed headersincluding an outlet header and an associated header, each of said secondpair of headers having a diaphragm means dividing the same into upperand lower chambers, a plurality of U-shaped, horizontally extendingtubes connecting the upper and lower chambers of said second pair ofheaders for establishing serially connected alternating parallel counterflow heat transfer steam path relative to said gas flow, said steamflowing from the upper chamber of said second mentioned associate headerto the upper chamber of said outlet header,

thence fromsaid upper outlet header chamber to the lower chamber of saidlatter associated header and then from said latter lower chamber-to thelower chamber of said outlet header, said latter U-shaped tubes beingdisposed in said cooler zone of said superheater cavity, and a pluralityof small diameter cross-over tubes connecting the upper chambers of theassociated headers of each section, so that said intermediate heatedsteam generated in said first section flows to said second section -tobe highly heated therein; said auxiliary furnace being disposedadjoining the hot zone of said superheater cavity so that the heatinggases flowing therefrom is utilized to highly superheat said steam.

16. For usein a marine boiler having a limited predeterminate effectivesuperheater heat absorption space in a gas, convection passhaving a hotzone and a relatively cooler. zone, the improvement of a superheaterhaving maximum heat absorption surfaces adapted to be positioned in saidlimited effective heat absorption space comprising a first superheatersection including a first pair of headers having a plurality of nestedU-shaped tubes connecting said headers for directing a steam flowbetween said headers, said tubes extending across the hot zone of saidspace; means for controlling the direction and velocity of the steamsflowing in said tubes between said headers whereby said steam isdirected in alternating parallel and counter-flow heat transfer passesrelative to the gas flow whereby said steam is superheated to anintermediate temperature; a second superheater section including asecond pair of headers having a plurality of nested U-shaped tubesconnecting the same for directing a steam flow therebetween, said lattermentioned U-shaped tubes being disposed in the cooler zone of saidspace; means controlling the direction and velocity of the steam flowthrough said tubes connecting said second pair of headers whereby saidsteam is directed in an alternating parallel and counter flow heattransfer steam flow relative to said gas flow and means connecting saidfirst and second sections in series whereby the intermediate superheatersteams generated in said first section is highly superheated in saidsecond section while metal temperatures of the superheater parts aremaintained below their high temperature corrosive limit, the velocity ofthe steam in the second section being greater than that in said firstsection to facilitate maintenance of tube temperatures in said secondsection.

:17. For use in a marine boiler having a limited predeterminateeflfective superheater heat absorption chamber in a gas convection pass,the improvement of a heat absorption chamber having adjacentprogressively decreasing gas temperature zones, a superheater havingmaximum heat absorption surfaces adapted to be positioned in saidlimited effective heat absorption chamber comprising a first superheatersection including a first pair of headers having a plurality of nestedU-shaped tubes connecting said headers for directing steam flow betweensaid headers, said tubes extending across the hottest portion of saidchamber, means for controlling the direction and velocity of the steamsflowing in said tubes between said pair of headers whereby said steamflows therebetween in alternating parallel and counterflow heat transferpasses relative to the gas flow for superheating the steam therein to anintermediate superheat temperature and a second superheater sectionincluding a second pair of headers having a plurality of nested U-shaped tubes connecting the same for directing a steam flowtherebetween, said latter mentioned U-shaped tubes being disposed in acooler portion of said chamber, means controlling the direction andvelocity of the steam flow through said tubes connecting said secondpair of headers whereby said steam is directed in an alternatingparallel and counter-flow heat transfer relative to said gas flow andmeans connecting said first and second sections in series whereby theintermediate superheater steams generated in said first section arehighly superheated in said section in a manner whereby metaltemperatures of the superheaterparts are maintained below their hightemperature corrosive limit, said velocity of the steam in the secondsection being greater than that in said first Section to facilitatemaintenance of tube temperatures in said second section. I

l8. A marine boiler consisting of a setting, an upper steam and waterdrum disposed centrally of. said setting, a lower water drum disposedlaterally of said'upper drum, a bank of inclined steam generating tubesconnecting said upper drum and laterally disposed lower drum, a pair oftransversely spaced water headers positioned below and parallel to saidupper drum, means for bottom supporting said spaced water headers,transversely spaced groups of vertically arranged screen tubesconnecting said spaced water headers to said upper drum and formingtherebetween a vertically elongated superheater cavity, refractory meanscooperating with said pair of spaced water headers to define a hopperbottom for said superheater cavity having its lowerend positionedbetween said spaced water headers, means forming an access opening forsaid hopper bottom between said spaced water headers, a main furnacechamber between said inclined tube bank and one of said groups ofvertically arranged screen tubes, means for firing said main furnace, asteam superheater having a multiplicity of horizontally arranged tubesdisposed in and extending substantially throughout the height of saidsuperheater cavity between said groups of vertically arranged screentubes, an auxiliary furnace chamber laterally adjoining the outer sideof said superheater tubes, said spaced water headers being arranged atapproximately the samelevel as the bottoms of said main and auxiliaryfurnace chambers, means for independently firing said auxiliary furnacechamber, and a single heating gas outlet flue at the outer side of saidinclined tube bank and arranged so that all of the heating gasesproduced in the main furnace are discharged directly to the flue afterflowing over said inclined tube bank and the heating gases from saidauxiliary furnace chamber are discharged to said outlet flue only afterflowing'over said superheater, through the main furnace chamber andacross said inclined tube bank.

References Cited in the file of this patent UNITED STATES PATENTS2,791,900 Banker July 2,

an ow

